This invention generally relates to thickening and stabilizing compositions of matter, compositions comprising thickening and stabilizing compounds and processes for thickening and stabilizing compositions of matter. More particularly, the invention relates to thickened compositions which are stabilized against the effects of oxidation or aging by the incorporation of antioxidant monomers into the polymeric thickeners.
Thickeners are commonly used in a wide variety of coating compositions, including latex paints. An effective thickener must be compatible with the overall composition. In the case of systems such as latexes, the thickener needs to be in a form which will not destabilize the dispersion of the latex particles.
Many types of thickeners are used. Water soluble thickeners include natural gums and resins like gum arabic, starch products, dextrins, alginates tragacanths and other such compounds. Synthetic thickeners include cellulose derivatives, polyvinyl alcohols, polyacrylamides, polyvinylpyrrolidione, various polyethers and their copolymers as well as polyacrylic acids and their salts. Some acrylic acid thickeners are described in U.S. Pat. Nos. 2,883,351; 2,956,046; 3,035,004; and 3,436,378.
A wide variety of oxidation stabilizers have been used for polymer-containing compositions, including amines, phenols, phosphites, sulfides, and metal salts. Hindered phenol antioxidants are frequently preferred because of their relatively slight tendency to stain or discolor. Compatibility with the variety of systems to be stabilized against oxidation has become an important factor. There is the need to overcome the tendencies of the antioxidant to migrate, evaporate, or separate from such systems as solid polymers or to form localized concentrations or to leaching from the systems when exposed to conditions like dry cleaning solvents, water, washing, weather or other forces which would encourage depletion of the antioxidant from the protected system. To control migration, evaporation and leaching in polymer systems it has been considered desirable to bind the antioxidants into the polymers either by copolymerization or, more often, by grafting.
Only a small portion of the approaches to solving the problems of forming antioxidants in polymeric form involve the use of antioxidant monomers having addition polymerizable unsaturation because these compounds have been difficult to make and purify as well as to polymerize in concentrations sufficient to impart antioxidant function to systems in which they might be used. Antioxidants like hindered phenols tend to be free radical scavengers or inhibitors; thus, they tend to inhibit free radical polymerization. Producing copolymers of hindered phenol monomers has often proven complex and expensive. Addition copolymers of most hindered phenol antioxidant monomers have been limited to less than about 10 percent antioxidant monomer (see U.S. Pat. No. 3,627,831, H. Huber-Emden, et al., Dec. 14, 1971; and Rubber Chem. Tech., 46, pp. 96-105, 106-114 (1973); R. Levy, Rev. Gen. Caout, Plast., 51(4), pp. 243-247 (1974).
In U.S. application Ser. No. 298,688, filed Sept. 2, 1981 and now abandoned, Mark R. Johnson taught an improved method of producing an addition polymerizable antioxidant with high activity, which need not have electronattracting groups on the phenolic ring. In the pertinent part, this process employs an unsaturated isocyanatoalkyl ester reacted with an active hydrogen of an antioxidant compound to form a urethane type of linkage. The reaction product has unsaturation for addition polymerization as well as the active antioxidant functionality. That application did not disclose incorporation of high levels of antioxidant monomers or use of the monomers in thickening compositions.
The inclusion of at least one unsaturated carboxylic acid monomer facilitates incorporation of antioxidant monomers into a copolymer, especially when the copolymer is produced in an emulsion system. At least 10 percent by weight of antioxidant may be included in the copolymer chain using the same polymerization techniques that have proven effective for monomers which do not inhibit oxidation or polymerization, when at least 15 percent by weight of an unsaturated carboxylic acid monomer is used. The use of at least 20 percent by weight of unsaturated carboxylic acid monomer with at least 0.10 percent by weight of antioxidant monomer produces a copolymer which acts as both a thickener and an antioxidant for the systems into which it is incorporated. When these copolymers are produced in an emulsion system, they are compatible with latexes. After incorporation into latexes or other aqueous systems, the copolymers may be solubilized by neutralization with base.